NC State Research Points the Way to More Energy-Efficient Devices

In a paper, researchers from North Carolina State University describe how they were able to reduce the coercivity of NFO films. Eventually, this could lead to more energy-efficient sensors, antennas, and other devices.

Researchers from NC State have paved the way to more energy-efficient high-frequency electronics, such as sensors, microwave devices, and antennas, by reducing the coercivity of nickel ferrite (NFO) thin films by as much as 80 percent.

By creating a corduroy pattern on the surface of NFO thin films, the researchers have been able to lower the coercivity of the NFO by 30 to 80 percent, depending on the thickness of the film. Thinner films experience a larger reduction in coercivity. The surface pattern on the NFO films consists of raised structures that are 55 nanometers high and 750 nm wide. The structures run parallel to each other and are spaced 750 nm apart, creating the corduroy effect.

“This technique reduces coercivity, which will allow devices to operate more efficiently, reducing energy use and improving device performance,” explained Goran Rasic, a PhD student at NC State and lead author of a paper describing the work. “We did this work on NFO but, because the reduced coercivity is a direct result of the surface patterning, we think our technique would work for other magnetic materials as well.”

The corduroy pattern on the surface of NFO thin films, which allowed researchers to reduce the coercivity of the NFO by as much as 80%. (Image courtesy of North Carolina State University)

Coercivity is a property of magnetized materials and is the amount of magnetic field needed to bring a material’s magnetization to zero. Basically, it is how much a material likes being magnetic. For devices that rely on switching current back and forth repeatedly -- such as most consumer electronics -- you want materials that have low coercivity, which improves device performance and uses less energy.

Iron oxides, like NFO, have a variety of properties that are desirable for use in high-frequency devices, but they do have high coercivity, which is a drawback.